5 Energy and Life
5.1
The Flow of Energy in Living Things (p. 104; Fig. 5.1)
A.
Most,
if not all, of a cell's activities require energy.
B.
Energy
is defined as the capacity to do work.
1.
Kinetic
energy is the energy of motion.
2.
Objects
that are not actively moving but have the capacity to do so possess potential
energy.
C.
Energy
can exist in a variety of forms (mechanical, heat, sound, electric current,
light, of radioactive radiation).
D.
Oxidation-Reduction
1.
Chemical
reactions involve making and breaking bonds between atoms.
2.
When an
atom or molecule loses electrons, it is oxidized (oxidation has occurred).
3.
When
an atom or molecule gains electrons, it is reduced (reduction has occurred).
4.
Energy
is transferred from one molecule to the next via oxidation-reduction (redox)
reactions.
5.2
The Laws of Thermodynamics (p. 105; Fig. 5.2)
A.
The First Law of
Thermodynamics
1.
The First Law of
Thermodynamics states that energy cannot be created or destroyed; it can only
undergo conversion from one form to another.
5.3
Chemical Reactions (p. 106; Fig. 5.3)
A.
The
molecules that react or combine are called reactants, or substrates, and the
result of the reaction is the products.
B.
Reactions
that tend to occur on their own are exergonic and release energy.
C.
Reactions
that need assistance to start are endergonic and require an energy boost.
D.
Activation
Energy
1.
Activation
energy is the energy needed in endergonic reactions to destabilize bonds and
cause the reaction to proceed.
E.
Catalysis
1.
Catalysis
is the process of lowering activation energy, which helps both endergonic and
exergonic reactions proceed more rapidly.
5.4
How Cells Use Energy (p. 109; Figs. 5.7, 5.8)
A.
Cells
need energy for moving organelles around inside the cell, for cell motility,
and for driving endergonic reactions.
B.
The
molecule in cells that supplies such energy is adenosine triphosphate (ATP).
C.
Enzymes
split ATP to drive endergonic reactions by coupled reactions in which the
endergonic reaction and the splitting of ATP occur together.
D.
Structure
of the ATP Molecule
1.
ATP
molecules are made up of a sugar, the base adenine, and three phosphate groups
that have high-energy bonds between them.
2.
Most
energy exchanges in the cell involve removing or adding on the terminal
phosphate group of the ATP molecule.
5.5
An Overview of Photosynthesis (p. 110; Fig. 5.9)
A.
The ultimate
source of energy on earth is energy from the sun, and less than 1% of the
energy from sunlight is captured by plants in photosynthesis.
B.
Photosynthesis
is carried out in chloroplasts and occurs in three phases: (1) sunlight energy
capture; (2) making ATP from the energy; and (3) using ATP to manufacture
organic compounds from carbon dioxide.
C.
The
first two phases are the light reactions, and the third involves the Calvin
cycle.
D.
Inside
the Chloroplast
1.
The
interior of the chloroplast is made up of internal membranes organized into
flattened sacs called thylakoids and a fluid substance called stroma.
2.
Chlorophyll
pigments are located in the thylakoids and are grouped together in a
light-capturing network called a photosystem.
3.
When
light waves of the correct wavelength strike chlorophyll molecules in the
photosystem, energy is passed from one chlorophyll molecule to the next until
it is eventually transferred from chlorophyll to a membrane-bounded protein
that will initiate one process of ATP production.
5.6
How Plants Capture Energy from Sunlight (p. 112; Figs. 5.10, 5.11, 5.12, 5.13)
A.
Specifically,
light energy travels in tiny packets called photons.
B.
We
perceive photons of energy only in the visible light range of the entire
electromagnetic spectrum.
C.
Pigments
1.
Pigments
are molecules capable of absorbing light.
2.
Retinal,
the pigment in human retinas, can absorb light in the violet to red range of
visible light.
3.
Plant
pigments, such as chlorophyll, also absorb and capture light energy.
4.
Accessory
pigments, like the carotenoids, absorb light energy in wavelengths not easily
absorbed by chlorophyll, and transfer the energy to the chlorophyll molecules.
5.7
Organizing Pigments into Photosystems (p. 114; Figs. 5.14, 5.15, 5.16, 5.17)
A.
The light
reactions of photosynthesis occur on membranes of the chloroplasts in three
stages; primary photoevent, electron transport, and chemiosmosis.
B.
Plants Use Two
Photosystems
1.
Plants employ two
photosystems in seriesm which generates power to reduce NADP+ to
NADPH with enough left over to make ATP.
5.8
How Photosystems Convert Light to Chemical
Energy (p. 116; Figs. 5.18,
5.19)
A.
Plants use the
two photosystems in a two-stage process called noncyclic photophosphorylation.
B.
For every pair of
electrons obtained from water, one molecule of NADPH and just over one molecule
of ATP are produced.
C.
Photosystem II
1.
The reaction
center of photosystem II the oxygen atoms of two water molecules bind to
magnesium, causing water to split.
2.
Oxygen is
released while electrons from water are used to replace those that are boosted
from the reaction center by sunlight.
D.
The Path to
Photosystem I
1.
The electron
boosted from photosystem II is carried to photosystem I by several
intermediates.
E.
Making ATP:
Chemiosmosis
1.
Protons cross the
thylakoid membranes at embedded proton pumps causing ADP to be phosphorylated
to ATP.
F.
Photosystem I
1.
The electron from
photosystem II is boosted to an even higher energy level as light strikes
photosystem I; the electron is passed to another carrier.
G.
Making NADPH
1.
Electrons
transported from photosystem I are used to reduce NADP+ to NADPH.
5.9
Building New Molecules (p. 118; Figs. 5.20, 5.21, 5.22)
A.
The
Calvin Cycle
1.
In C3
photosynthesis, plants use the Calvin cycle in the stroma of the chloroplasts
to assemble carbon molecules, such as glucose.
2.
The assembly
of these molecules is carried out by the Calvin cycle, an enzyme-catalyzed
pathway.
3.
ATP
drives the endergonic reactions while NADPH from photosystem I provides a
source of hydrogens and the energetic electrons needed to bind them to carbon
atoms.
5.10
An Overview of Cellular Respiration (p. 120; Figs. 5.23, 5.24, 5.25)
A.
Plants
store energy from sunlight in the form of organic compounds, but all other
organisms, plants included, must oxidize the organic compounds, using a process
known as cellular respiration to supply the energy needed to drive cellular
activities.
B.
Aerobic
Respiration
1.
The
first stage of cellular respiration, called glycolysis, occurs in the cytoplasm
of the cell, needs no oxygen, and can be carried out by every living creature.
2.
The
second stage, oxidation, occurs in mitochondria, which only eukaryotes possess.
3.
Oxidation
uses oxygen as the final electron acceptor.
C.
Anaerobic
Respiration
1.
Sulfur bacteria
derive energy from the reduction of inorganic sulfates.
5.11
Using Coupled Reactions to Make ATP (p. 122; Figs. 5.26, 5.27, 5.28)
A.
Glycolysis
1.
Glycolysis
is a biochemical pathway that involves a sequential series of ten
enzyme-catalyzed reactions.
2.
During
glycolysis, two coupled reactions also occur, leading to the production of ATP
via substrate-level phosphorylation.
3.
In
addition, two electrons are carried by NADH to the electron transport chain.
4.
Glycolysis
ends up with two pyruvic acid molecules; these are transported into the
mitochondria where they are converted to acetyl coenzyme A and will enter the
Krebs cycle of oxidation.
B.
Fermentation
1.
In
the absence of oxygen, fermentation, rather than oxidation, is the pathway that
occurs after glycolysis.
2.
Fermentation
yields lactic acid in muscle tissue.
3.
In
some organisms, such as yeasts, fermentation yields alcohol.
5.12
Harvesting Electrons from Chemical Bonds (p. 125; Figs. 5.29, 5.30, 5.31, 5.32)
A.
The Krebs Cycle
1.
The Krebs cycle
takes place in the mitochondria and involves three steps.
2.
In the first
step, acetyl-CoA joins the cycle, binding to a four-carbon molecule to produce
a six-carbon molecule.
3.
Second, two
carbons are removed as CO2, their electrons donated to NAD+,
and a four-carbon molecule is left.
4.
Third, more
electrons are extracted, and the four-carbon starting material is regenerated.
5.
In the process of
cellular respiration, glucose is entirely cleaved.
6.
All that is left
over are six molecules of CO2 and energy in the form of four ATP
molecules and the electrons carried by 10 NADH and 2 FADH2 carriers.
5.13
Using Electrons to Make ATP (p. 128; Figs. 5.33, 5.34, 5.35)
A.
Mitochondria use
chemiosmosis to make ATP.
B.
Moving Electrons
Through the Electron Transport Chain
1.
The NADH
molecules carry their electrons to the inner mitochondrial membrane where they transfer
the electrons to a series of membrane-associated proteins known as the electron
transport chain.
C.
Building an
Electrochemical Gradient
1.
The matrix of the
mitochondrion contains the enzymes that carry out the reactions of the Krebs
cycle.
2.
As electrons are
passed down the electron transport chain, the energy they release transports
protons out of the matrix and into the outer compartment (the intermembrane
space).
3.
Proton pumps,
driven by energy from the electrons in the electron transport chain, in the
inner mitochondrial membrane accomplish this.
D.
Producing ATP:
Chemiosmosis
1.
As the proton
concentration in the outer compartment rises above the matrix, the matrix
develops a negative charge.
2.
This negative
charge attracts the positively-charged protons and induces them to enter the
matrix.
3.
The protons pass
through special proton channels driven by a diffusion force called
chemiosmosis.
4.
As the protons
pass through these channels, ATP is produced from ADP plus PI in the
matrix.
5.14
A Review of Cellular Respiration (p. 130; Fig. 5.36)
A. Through cellular respiration, then,
one molecule of glucose generates a total of 36 ATP.
B.
Regulating
Cellular Respiration
1.
The
rate of ATP production slows when your body has an ample supply.
2.
The control
works through a system of feedback inhibition in which key enzymes in the Krebs
cycle have an allosteric site to which ATP molecules become stuck.
3.
The
binding of ATP molecules causes the enzyme to change its shape and not function
as an enzyme.
Chapter 29 Ecosystems
29.1
Trophic
Levels (p. 686; Figs. 29.1, 29.2, 29.3)
A.
What Is an Ecosystem?
1.
Ecology is defined as the
study of the interactions of living organisms with each other and with their
physical surroundings.
2.
A community is the group of
different living creatures that inhabit an area and interact with each other.
3.
Where the community lives is
defined as the habitat.
4.
The community together with
its habitat comprises an ecosystem.
B.
The Path of Energy: Who Eats Whom in Ecosystems
1.
Each member of a community uses
energy, the ultimate source of which is sunshine striking the earth.
2.
Photosynthetic organisms,
plants and algae, capture the energy in sunlight and incorporate it into
organic compounds and are the producers of communities.
3.
All other organisms are consumers
that obtain their energy either by eating plants or by eating each other.
4.
Each organism can be assigned
to a feeding level, known as a trophic level.
5.
Plants are trophic level 1;
consumers eating plants (primary consumers) are in trophic level 2; and
consumers eating plant-eaters (secondary consumers) are in trophic level 3.
6.
If these organisms are
arranged in a linear fashion, they make up a food chain.
7.
In most communities, however,
the feeding relationships among organisms are highly complex, and make up a
food web.
C.
Producers
1.
Plants use energy from the sun to build energy-rich
sugar molecules.
2.
Plants also remove nitrogen and other nutrients from
soil and incorporate them into plant tissues.
D.
Primary consumer
1.
Herbivores (primary consumers)
eat a variety of different kinds of plants.
E.
Secondary consumer
1.
Carnivores (secondary
consumers) may choose from a number of food items, depending on what is
abundant and what they decide to chase down to catch.
2.
Omnivores make food webs even
more complex because, like humans, they eat a variety of plants and animal
tissues.
F.
Detritivores and Decomposers
1.
Detritivores and decomposers eat dead or dying organisms
and recycle nutrients back to the soil.
29.2
Energy Flows
Through Ecosystems (p. 689; Figs. 29.4, 29.5)
A. The amount of energy fixed by producers in the ecosystem is
the primary productivity.
B. Plants also use much of the energy they store in organic
compounds, so net primary productivity must be calculated to account for that
loss of energy.
C. The total weight of all organisms in the ecosystem is the
biomass.
D. Some ecosystems, like cattail swamps, have a very high net
primary productivity and a moderate biomass.
E. Others, like a tropical rain forest, have a high net
primary productivity and an extremely high biomass.
F. A food chain cannot be made up of more than four or five
lengths because of a great deal of energy, usually around 90%, that is lost at
each trophic level.
29.3
Ecological
Pyramids (p. 690; Fig. 29.6)
A. The
biomass and numbers of the producers is always greater than that of the
consumers in any ecosystem.
B.
This relationship can be shown using an ecological
pyramid of numbers or biomass.
C.
Inverted Pyramids
1.
Some aquatic pyramids are inverted because they are
dominated by a small biomass of photosynthetic plankton that have a very high
rate of turnover.
D.
Top Carnivores
1.
The loss of energy that occurs at each trophic level
places a limit on the number of top-level carnivores a community can support.
2.
Top-level carnivores also tend to be larger animals, so
the small biomass available at the top of the pyramid is concentrated into a
few individuals.
29.4
The Water
Cycle (p. 691; Figs. 29.7, 29.8)
A. Unlike
energy, materials within ecosystems are recycled from one component to the
next.
B.
The paths of water, carbon, and soil nutrients are
closed circles, or cycles.
C.
Water cycles through
ecosystems.
1.
The water cycle has an
environmental component and an organismic component.
D.
The Environmental Water Cycle
1.
The environmental water cycle
involves evaporation from water surfaces and condensation of water vapor that
falls as rain or snow on land.
2.
It runs off the surface of
the land back to the lakes and oceans.
E.
The Organismic Water Cycle
1.
Plants are the primary
component of the organismic water cycle.
2.
Plants take up water from the
soil, and much of it passes through the plant and is given off at the leaves by
transpiration.
F.
Breaking the Cycle
1.
In tropical rain forests, a
great amount of water is moved via transpiration, causing localized rainfall.
2.
When humans deforest areas,
they become desertlike because plants are no longer present to recycle water.
G.
Groundwater
1.
Groundwater can be found
beneath the surface of the earth in aquifers.
2.
People in the
3.
Unlike surface water that is
continually renewed, groundwater recharge rates are slow, and pollutants remain
trapped in groundwater virtually forever.
29.5
The Carbon
Cycle (p. 693; Fig. 29.9)
A. Carbon
is captured from its reservoir, atmospheric carbon dioxide, by plants through
photosynthesis.
B.
Plants take up carbon dioxide
and incorporate it into organic compounds.
C.
Carbon cycle is returned to
the atmosphere through respiration, combustion, and erosion.
D. Respiration
1.
Plants and animals give off
carbon dioxide as a by-product of cellular respiration, so carbon is returned
to the atmosphere.
E.
Combustion
1.
When we burn wood or fossil
fuels, carbon trapped long ago is released to the atmosphere.
29.6
The Nitrogen
Cycle (p. 694; Fig. 29.10)
A.
Much nitrogen exists in the
atmosphere, but is unavailable for plants.
B.
Nitrogen fixation is one
method by which nitrogen can be moved from the atmosphere to the soil where
plants can use it.
C.
Several groups of bacteria
can fix nitrogen, but they must be protected from oxygen in order to carry out
that process.
D.
Bacteria are encased in cysts
or in root nodules of certain types of plants, called legumes, to allow them to
carry out nitrogen fixation without the presence of oxygen.
E.
Industrial fixation of
nitrogen now accounts for up to 30% of the nitrogen cycle.
29.7
The
Phosphorus Cycle (p. 695; Fig. 29.11)
A. Available supplies of phosphorus are taken up from soils by
plants and passed along the food chain.
B. When organisms die, the phosphorus they contain is recycled
back to the soil.
29.8
Latitude and
Elevation (p. 697; Figs. 29.14, 29.15)
A. Temperature
also varies with elevation, with higher altitudes experiencing cooler
temperatures.
B.
Rain Shadows
1.
When air blows across the
water, the warmth and moisture are carried out onto the land.
2.
The locations of mountains
affect climate locally.
3.
On the wind side of
mountains, air cools as it is pushed upward, and water condenses and falls to
the earth.
4.
On the back side of the
mountains, a rain shadow develops where rainfall is scant.
29.9Land Ecosystems (p. 704; Figs. 29.25,
29.26, 29.27, 29.28, 29.29, 29.30, 29.31, 29.32, 29.33)
C. A
biome is a terrestrial ecosystem that occurs over a broad area and is
characterized by a particular combination of climate and organisms.
D. The world can be divided into seven major climate regions,
thus there are seven major biome types.
E. Seven
minor, or less widespread, types of biomes also are found: polar ice, mountain
zone, temperate evergreen forest, warm/moist evergreen forest, tropical monsoon
forest, chaparral, and semidesert